The present description is directed to purification and filtering systems and methods and, more particularly, to purification and filtering systems, apparatus, and methods that have enhanced efficiency in terms of removing suspended contaminants in a gaseous medium, such as air.
Several air and gas particle purification and filtering systems and methods are known for purifying and filtering air of contaminants, such as odors, gases, smoke, pollen, dust, etc. Room air purifiers utilize filter elements that may include electrostatically charged fibers, since the latter have relatively high efficiencies for capturing charged particles from air passing through the filters.
One commercially available type is a room air purifier. Some room air purifiers are portable and include a filtration system, a fan, and a device for charging air molecules and particles. The filtration system typically includes a filter element(s) positioned intermediate or between intake and exhaust passages. A fan unit typically draws ambient air into the air purifier and through the filter elements before expelling it from the exhaust; in other embodiments the fan may draw air into the intake and then force air through the filter before passing through the exhaust. Often, in room air purifiers of this kind an ionizer generates ions in the flowing air stream for charging molecules in the air. Generated ions may be of positive polarity, negative polarity or a combination of both negative and positive polarity. Included in such approaches are high voltage electrodes in the form of wires(s), point(s), or brush(es) and the like. For example, the high voltage may be in the order of about +/−4-20 kV when measured with a high voltage meter having a 1 GΩ input impedance and about +/−4-30 kV when measured with a high voltage meter having 10 GΩ input impedance. The ionized air molecules within and exiting the air purifier are understood to rapidly transfer their charge to airborne contaminants including particles, odors, gases and the like. Some of the air and gas contaminants charged by the ionized air molecules become, through agglomeration, too heavy to remain in air and, hence, settle or precipitate to ground. Other charged contaminants are attracted to room surfaces (e.g., walls, etc.) surrounding the air purifier, and still others are drawn back into the air purifier by the suction of the fan to be trapped by the filter elements within the room air purifier. In some room air purifiers, the filter elements may be electrostatically charged so as to be particularly receptive to attracting electrostatically charged contaminants and this thereby increases removal efficiency. An example of this latter type of air purifier is commercially available from 3M Corporation, St. Paul, Minn. under the trade name FAP04-RC Ultra-Slim Air Purifier.
It has been determined that particle removal efficiencies of known air purifiers vary over a period of time. It is believed that such variations are at least a function of variations in ionization of the air passing through the room air purifier. The ionized species tend to accumulate or build-up on the surrounding surfaces of the air purifier. As such, these voltage fields tend to collapse which tends to lessen the efficiency of the overall performance since the flow of electrons and ion current decrease.
Known approaches have been attempted to provide for more consistent ionization of the flowing air. Some have used a brush to generate ions coupled with a reference ground wire to the interior of the housing near the ionizer discharge, that is a wire that is not attached to earth ground, but rather provides the low voltage reference from the ionizer transformer against which the high-voltage circuit is stepped-up. The ground wire created an isolated point ground. It has been determined that the foregoing point ground arrangement yielded inconsistent ionization results, as measured by inconsistencies in generally expected measurements of a Clean Air Delivery Rate (CADR) for small particles, such as 1 micron or less as, for example, tobacco smoke and combustion by-products.
Another approach included adding several strips of conductive tape on and around PC boards in an outlet of the air purifier and connecting them to the reference ground from the ionizer power supply. This arrangement did not appear successful in providing tangible benefits to the CADR.
Still another approach included using an exposed conductive strip several inches long (e.g., 7.5 inches) upstream of the ionizer discharge and connected to the interior of the housing. The exposed ground strip yielded erratic results and when a filter was installed, the ionizer discharge had no line of sight to ground source. This approach also did not yield results that improved the consistency of ionization across the discharge.
Other grounding schemes in air purifiers include a high voltage discharge electrode upstream of an exhaust outlet and a capped metal pin which is located normal to the discharge with respect to the airflow. A plastic shroud blocks direct line of sight between the discharge and ground pins. This kind of air purifier tends to be less effective at removing submicron contaminants and additionally some of such contaminants accumulate on the shroud and such accumulation may provide a conductive pathway between the high-voltage electrode and ground, thereby potentially providing a partial short circuit as well as a decrease in performance over extended periods of time.
Accordingly, none of the heretofore known air purifiers are as efficient over a period of time as could otherwise be desired because of their transitory effectiveness. Accordingly, there is a need for air purifier and methods associated therewith that are particularly useful for prolonging the effectiveness of the gas or air purification system so as to make them as efficient as could otherwise be desired.